This application is based on Japanese Patent Application Nos. 2001-055563 filed Feb. 28, 2001 and 2002-050389 filed Feb. 26, 2002, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus, a calibration method and a calibration chart printing method, and more specifically to a chart that is printed for a calibration which makes a printing characteristic of an ink jet printing apparatus predetermined one.
2. Description of the Related Art
In a printing apparatus widely used for printing characters and images, density and a hue of printed images may change depending on a variation in a condition of an environment, in which the printing apparatus is used to operate, such as temperature and humidity, and on a difference in characteristics of printing materials such as ink and of printing medium such as printing papers. The density of the printed image may also vary from one apparatus to another. Further, these characteristic variations and differences also may be caused by ageing of parts from which the printing apparatus is composed. To cope with such variations in the printing characteristic, a calibration, in which for example a predetermined image processing parameter such as a gamma correction table is changed, has been known to be performed to make the printing characteristic predetermined one.
The calibration includes a processing causing the printing apparatus to print for example a chart arranging patches of a plurality of density levels to determine the printing characteristic of that apparatus. Then, the processing causes a reading apparatus such as a color measuring device to measure densities of patches and changes the contents of the image processing parameters such as the gamma correction table based on the measured density values of the patches.
In a printing apparatus of an ink jet method it is known to be observed that a solvent of ink such as water evaporates through ink ejection openings in a printing head to increase a viscosity of ink, though there is variation in degree of the increasing. This may result in ejection failures, such as ejected ink droplets decreasing in amount and deviating from an intended direction. Even when the ink is ejected normally, the evaporation of the ink solvent may increase a concentration of a coloring material of ink, such as dye or pigment, to a higher-than-normal level. Hence, when there are such ejection failures and increased dye densities at time of printing patches in the calibration, this means that the same ink ejection condition as the actual printing operation is not realized. The result of measurement of such printed patches therefore may not accurately represent the printing characteristic of the apparatus during the actual printing.
Generally, the ink jet printing apparatus, when the printing is not performed, covers a surface of the printing head provided with the ink ejection openings with a cap so as to restrain the ink solvent from evaporating to prevent an increase in the viscosity of ink. It is noted, however, that if the cap is constructed to seal the ejection opening-formed surface completely air-tight, a capping action of the cap to the printing head increases the pressure within the cap and destroys ink meniscuses formed near the ejection opening, leading to ink leakage and unstable ink ejection. For this reason, the cap is generally formed with a hole to communicate its interior with the open air or the capping is done in such a manner as to form a clearance. However, when the printing is not performed for a long period of time, the ink solvent vaporizes, though in small amounts, through the hole or the clearance. There is a correlation between the amount of ink solvent evaporated and the time that the apparatus is left unused. The increase in ink viscosity and in dye concentration due to the solvent evaporation proceeds from the ejection opening toward an interior of an ink passage as the time that the apparatus is left unoperated increases.
As the described above, the ink jet printing apparatus may have decreasing in the ink ejection volume and increasing in the coloring material concentration due to the evaporation of ink solvent, though there is variations in the degree of the decreasing or the increasing. When the degree of the reduction in the volume of ink ejected and the increase in the coloring material concentration are relatively small, the effect they have on the image printed by the normal printing operation cannot be recognized by naked eye. However, the chart printed during the calibration is measured for density as by a color measuring device or the like, so even when the ejection amount reduction and the coloring material concentration increase are relatively small, they are recognized in the measuring process as significant density differences or color differences. Therefore, the calibration data obtained from such a measurement does not precisely represent the printing characteristic of the apparatus. It is thus difficult to perform a precise calibration.
As a means for removing ink of increased viscosity and increased coloring material concentration, a so-called preliminary ejection is known which ejects a predetermined amount of ink at a predetermined location in the apparatus, for example, before starting the printing operation. Since the preliminary ejection in general is intended to remove those portions of ink at or near the ejection opening which have the increased viscosity and the increased concentration of coloring material, the amount of ink ejected during the preliminary ejection is small, and accordingly not enough to remove all the ink whose viscosity and coloring material concentration have increased relatively significantly over a long period of time during which the apparatus has been left unoperated.
As a means that can remove ink whose viscosity and coloring material concentration have increased to a significant extent, a recovery mechanism is known which discharges ink by drawing it by suction or pressurizing the interior of the printing head through the ink ejection openings. Hence, when printing a color chart for calibration, it is considered that this recovery mechanism can be activated to perform a recovery operation to ensure an accurate calibration.
However, when the calibration is carried out relatively frequently, the recovery operation is also performed similarly frequently to cause a problem associated with the waste ink discharged from the head. For example, in a printing apparatus which provides a reference for color calibration, because high precision in a color reproduction or a gradation level reproduction is required, the number of times that the calibration is performed increases. In that case, a disposal of the ink discharged as a result of the recovery operation for calibration raises an issue.
More specifically, the ink that is removed by the recovery mechanism by suction or pressurization is generally absorbed by a waste ink absorbent in the apparatus for natural drying. When the calibration is done frequently, the absorbent needs to have a sufficient capacity to absorb a greater amount of ink discharged by the recovery operations than can be dried naturally. This in turn increases the size of the apparatus.
When the apparatus is configured to discharge the ink into a container such as a waste ink tank, similar problems arise. That is, not only does the provision of a sufficient ink holding capacity increase the size of the apparatus, a separate new mechanism or new processing is required for processing the waste ink collected.
An object of the present invention is to provide an ink jet printing apparatus, a calibration method and a calibration chart printing method which can execute a highly precise calibration without processing for waste ink resulting from a recovery operation.
In the first aspect of the present invention, there is provided an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the apparatus comprising:
printing means that prints a chart for a calibration of the ink jet printing apparatus by causing the printing head to eject the ink to the printing medium,
wherein the chart includes a patch to be measured by a measurement device and a pattern which is printed before the patch and is printed at an ejection duty equal to or higher than a maximum ejection duty in an ejection duty, at which the patch is printed.
In the second aspect of the present invention, there is provided an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the apparatus comprising:
printing means that prints a chart for a calibration of the ink jet printing apparatus by causing the printing head to eject the ink to the printing medium,
wherein the chart includes a patch to be measured by a measurement device and a pattern which is printed before the patch and is printed at a predetermined ejection duty and as the pattern of a predetermined size.
In the third aspect of the present invention, there is provided a calibration method for calibrating an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the method comprising the steps of:
printing a chart for a calibration of the ink jet printing apparatus by causing the printing head to eject the ink to the printing medium;
executing a measurement of the chart by using a measurement device;
generating calibration data based on a result of the measurement; and
changing predetermined data for printing, based on the generated calibration data,
wherein the chart includes a patch to be measured by the measurement device and a pattern which is printed before the patch and is printed at an ejection duty equal to or higher than a maximum ejection duty in an ejection duty, at which the patch is printed.
In the fourth aspect of the present invention, there is provided a calibration method for calibrating an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the method comprising the steps of:
printing a chart for a calibration of the ink jet printing apparatus by causing the printing head to eject the ink to the printing medium;
executing a measurement of the chart by using a measurement device;
generating calibration data based on a result of the measurement; and
changing predetermined data for printing, based on the generated calibration data,
wherein the chart includes a patch to be measured by the measurement device and a pattern which is printed before the patch and is printed at a predetermined ejection duty and as the pattern of a predetermined size.
In the fifth aspect of the present invention, there is provided a method of printing a chart used for a calibration to calibrate an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the method comprising the step of:
printing the chart by causing the printing head to eject the ink to the printing medium,
wherein the chart includes a patch to be measured by a measurement device and a pattern which is printed before the patch and is printed at an ejection duty equal to or higher than a maximum ejection duty in an ejection duty, at which the patch is printed.
In the sixth aspect of the present invention, there is provided a method of printing a chart used for a calibration to calibrate an ink jet printing apparatus, which uses a printing head for ejecting ink, ejecting the ink to a printing medium so as to perform printing, the method comprising the step of:
printing the chart by causing the printing head to eject the ink to the printing medium,
wherein the chart includes a patch to be measured by a measurement device and a pattern which is printed before the patch and is printed at a predetermined ejection duty and as the pattern of a predetermined size.
With the configuration described above, a calibration chart is printed that includes patches to be measured by a measuring device and a pattern printed, prior to the printing of the patches, at an ejection duty equal to or higher than a maximum ejection duty of the patches. This chart printing allows the amount of ink ejected for printing the pattern of the chart from the printing head to be set larger than that of a normally executed preliminary ejection by properly determining the ejection duty and the shape (or size) of the pattern, and to be made just enough to remove the ink which has a relatively high viscosity and an increased coloring material concentration. This can prevent the patches to be measured from being printed with ink whose viscosity and coloring material concentration are higher than normal, and then the patches can be printed, which faithfully reflect the printing characteristic of the printing head or the like at time of printing.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.